Network providers have always been pursuing the implementation methods of carrying services of voice, video, data, private line, etc., over the same network at the same time so as to increase the utilization of network and reduce the costs of investment and operation.
An IP (Internet Protocol) network has the advantages of high efficiency of bandwidth utilization, low price, and high bandwidth, and is open and easy for providing flexible services. With the mass deployment of broadband access network, the IP network gradually becomes the practical platform for carrying integrated services. Providers wish to access voice, video and enterprise private line and the like, besides the originally carried data services, via the broadband access nodes. In addition to IP-based voice and enterprise private line which are newly deployed on the broadband network, some providers also wish to carry the traditional services, such as voice or private lines based on TDM (Time Division Multiplexing), ATM (Asynchronous Transfer Mode), or FR (Frame Relay), via the broadband access network.
The existing IP network is mainly designed and constructed for the transmission of data services. The IP network is connectionless and can meet the requirement of the transmission of data services which need only reachability, but can not meet the requirements of reliable transmission (packet loss ratio), time characteristics (order, delay and delay variation), security (isolation between various services, privacy of private network services) and survivability (the recovery time of backup link after failure) for transmission of voice, video and private line interconnection services.
In order to meet the requirement of QoS (quality of service) required by the transmission of voice, video and private line interconnection services, it is necessary for a bearer network to provide connection-oriented service for these services, and protect these services on the basis of connection. To this end, the IP network needs to provide a connection-oriented bearer service.
The MPLS (Multi-Protocol Label Switching) technology is a new technology for providing connection over the IP network. The MPLS technology has been applied to the broadband core network and can provide connection-oriented bearer service. At present, however, the MPLS technology is applied only for the broadband core network; while for an access network, different access approaches are employed to implement the access of different types of services over the access network.
At present, these different types of services are generally transmitted over different independent access networks established respectively for the services of voice, video, data and private lin.
The voice service is accessed by PSTN (Public Switched Telephone Network, the ordinary telephone network using TDM technology). SDH (Synchronous Digital Hierarchy) system is used for the networking of the accessing network;
The data service is accessed by broadband. Direct fiber connection, Ethernet ring (using RSTP (Rapid Spanning Tree Protocol) for protection) or RPR (Resilient Packet Ring) are employed for the networking of the accessing network;;
The video service is accessed by CATV (Cable TeleVision) system. CATV system is employed for the networking of the accessing network;;
The private line service is accessed by DDN (Digital Data Network, which is a private line technology based on TDM), ATM or FR network. SDH system is employed for the networking of the accessing network.
It can be seen that, presently, if a variety of services are to be transmitted, investment for the corresponding network establishment are needed respectively, and the individual networks need to be maintained independently, which increases the provider's CAPEX (Capital Expenditures) and OPEX (Operating Expenditures).
At present, an access network may use the MSTP (Multi-service Transport Platform) system based on SDH, to carry the data, voice and private line altogether.
However, MSTP is a technology based on SDH, with low availability of bandwidth, poor flexibility of services, complex administration and maintenance, and high costs for networking and maintenance.
Another way for implementing integrated service access network is based on ATM, that is, data, voice and private line can be carried together over the ATM network.
However, with the enlargement of IP network, more and more applications have been transplanted to IP platform to make use of its advantages. The ATM network is not the actual development direction of network. It has low efficiency, high cost, and poor expandability, and is difficult to implement whole-network and whole-path coverage when carrying the IP services. ATM is also difficult to implement video multicast services. Furthermore, when ATM network is applied, two kinds of networks based on ATM protocol and IP protocol need to be maintained, thus complicating the administration and maintenance. So, the ATM network can not serve as the integrated service bearer platform for all services covering whole network and whole path in the aspects of bandwidth, scale and tendency, etc.
Presently, the access network based on Ethernet protocol is also employed. That is, the Ethernet technology is applied between a broadband access node and a broadband access server to carry the services of data, voice, video and private line together.
With the Ethernet access network, the access of pure data services can be implemented simply and efficiently at a low cost. However, there are still some issues in the bearing of integrated services.
1. survivability: the Ethernet access network of tree networking can not meet the requirements for service protection. The protection switching time of an Ethernet ring network constructed with RSTP protocol is at the level of seconds, which can not meet the switching time requirements for high quality services.
2. QoS (Quality of Service) and security: the Ethernet forwarding based on MAC (Media Access Control) address learning can not meet the security requirements for the bearing of integrated services, because its forwarding direction is unpredictable, and traffic cannot be isolated completely, and can not meet the QoS requirements for the bearing of integrated services, because bandwidth is hard to be planned.
3. A whole-network and whole-path connection across BAS (Broadband Access Server) or edge router of core network, which ensures a better quality of service for voice and private line, can not be established.
4. The traditional services of TDM, ATM, FR can not be carried, there is no standard method for carrying TDM, ATM, FR across the BAS or the edge router of core network on Ethernet.
Therefore, at present, there is no unified access network which can access all the existing services, such as voice, data, video and private line, etc., at the same time with a low cost.